Heterogeneous photocatalysis using TiO2 modified with hydrotalcite and iron oxide under UV–visible irradiation for color and toxicity reduction in secondary textile mill effluent

• Autor(a) principal: Arcanjo, Gemima Santos
• Data de Publicação: 2018
• Outros Autores: Mounteer, Ann H., Bellato, Carlos Roberto, Silva, Laís Miguelina Marçal da, Dias, Santos Henrique Brant, Silva, Priscila Romana da
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: https://doi.org/10.1016/j.jenvman.2018.01.033; http://www.locus.ufv.br/handle/123456789/18266
• topic: ADMI; Daphnia similis; Reactive dyes; Tertiary treatment

The objective of this study was to evaluate ADMI color removal from a biologically treated textile mill effluent by heterogeneous photocatalysis with UVevisible irradiation (UVevis) using a novel catalyst composed of TiO 2 supported on hydrotalcite and doped with iron oxide (HT/Fe/TiO 2 ). Simulated biological treatment of solutions of the dyes (50 mg/L) used in the greatest amounts at the mill where the textile effluent was collected resulted in no color removal in reactive dye solutions and about 50% color removal in vat dye solutions, after 96 h, indicating that the secondary effluent still contained a large proportion of anionic reactive dyes. Photocatalytic treatments were carried out with TiO 2 and HT/Fe/TiO 2 of Fe:Ti molar ratios of 0.25, 0.5, 0.75 and 1, with varying catalyst doses (0e3 mg/L), initial pH values (4 e10) and UVevis times (0e6 h). The highest ADMI color removal with unmodified TiO 2 was found at a dose of 2 g/L and pH 4, an impractical pH value for industrial application. The most efficient composite was HT/Fe/TiO 2 1 at pH 10, also at a dose of 2 g/L, which provided more complete ADMI color removal, from 303 to 9 ADMI color units (96%), than unmodified TiO 2 , from 303 to 37 ADMI color units (88%), under the same conditions. Hydroxyl radicals were responsible for the color reduction, since when 2- propanol, an OH scavenger, was added color removal was very low. For this reason, the HT/Fe/TiO 2 1 composite performed better at pH 10, because the higher concentration of hydroxide ions present at higher pH favored hydroxyl radical formation. COD reductions were relatively low and similar, approximately 20% for both catalysts after 6 h under UVevis, because of the low initial COD (78 mg/L). Secondary effluent toxicity to Daphnia similis (EC 50 1⁄4 70.7%) was reduced by photocatalysis with TiO 2 (EC 50 1⁄4 95.0%) and the HT/Fe/TiO 2 1 composite (EC 50 1⁄4 78.6%). HT/Fe/TiO 2 1 was reused five times and still lowered secondary effluent ADMI color below local discharge limits. Benefits of the HT/Fe/TiO 2 1 catalyst compared to TiO 2 include its lower bandgap energy (2.34 eV vs 3.25 eV), higher ADMI color removal and its magnetic nature that facilitated its recovery and would reduce treatment costs.